CVD processing requires a number of vaporized processing liquids. These vaporized liquids are generated and supplied to a CVD chamber via a system of pipes (or "lines") and vaporizing mechanisms known as a gas delivery system. Typically a separate vaporizing mechanism is provided for vaporizing each processing liquid, and is coupled to a source of processing liquid and a source of carrier gas. Each vaporizing mechanism and processing liquid source combination within a gas delivery system is referred to as a vaporization stage. Although a number of vaporizing mechanisms exist (e.g., bubblers, injection valves, etc.), most conventional gas delivery systems employ a plurality of injection valves for vaporizing processing liquids to be delivered to a CVD chamber.
A typical injection valve comprises a vaporization region which is coupled to a processing liquid inlet for receiving a pressurized processing liquid, to a carrier gas inlet for receiving a pressurized inert carrier gas, and to an outlet for delivering a vaporized processing liquid/carrier gas mixture. The processing liquid inlet, by necessity, is small in size so as to maintain a low partial vapor pressure of the processing liquid in the carrier gas. The injection valve is heated such that when the processing liquid is injected into the carrier gas, the heat and the low partial vapor pressure of the processing liquid in the carrier gas causes the processing liquid to vaporize.
The processing liquid inlet's small size renders the processing liquid inlet susceptible to clogs which result from residue produced when processing liquid reacts with moisture or other contaminants in the gas delivery system. Thus, maintenance of conventional gas delivery systems is expensive due to injection valve clogging. A clogged injection valve can cause downtime not only of the chamber to which the clogged injection valve is coupled, but also of upstream and/or downstream chambers. In addition to costly chamber downtime, injection valves themselves are expensive, typically costing more than two thousand dollars to replace, exclusive of labor costs. Considerable effort has been devoted to developing clog resistant gas delivery systems, and numerous advances have been achieved.
A particularly worthy advance is the recognition by Applied Materials, Inc., that alloys containing nickel react with the CVD processing liquid TEPO, causing residue formation and clogging, and the recognition that chromium can repress the nickel/TEPO reaction. Thus, gas delivery components made with less than 1% nickel and with 16-27% chromium significantly reduce clogging as described in commonly assigned U.S. Pat. No. 5,925,189 (application Ser. No. 08/568,193, filed Dec. 6, 1995, AMAT No. 888/PDD/KPU8/MBE). Despite such advances, injection valve clogging remains a problem, particularly when a gas delivery system must be configured with existing nickel-containing components.
Accordingly, a need exists for a clog resistant injection valve and for a gas delivery system that can be easily and inexpensively cleaned of residue, and that resists clogging regardless of component composition.